Get the registers that are being used by this instruction.
regUsage doesn't need to do any trickery for jumps and such.
Just state precisely the regs read and written by that insn.
The consequences of control flow transfers, as far as register
allocation goes, are taken care of by the register allocator.

Make an unconditional jump instruction.
For architectures with branch delay slots, its ok to put
a NOP after the jump. Don't fill the delay slot with an
instruction that references regs or you'll confuse the
linear allocator.